Management of component carriers based on time segment coordination

ABSTRACT

A method and system for managing time segments per subframe used for downlink control channel communication by adjacent base stations that each provide carrier-aggregation service on first and second component carriers. The base stations may work with each other to differentially structure the component carriers, such that the base stations use different time segments than each other for downlink control channel communication on the first component carrier but the same time segments as each other for downlink control channel communication on the second component carrier. Further, based on this differential structuring, the base stations may then schedule transmission of one type of data on the first component carrier and another type of data on the second component carrier.

REFERENCE TO RELATED APPLICATION

This disclosure is related to the disclosure of U.S. patent applicationSer. No. 14/531,628, filed Nov. 3, 2014, the entirety of which is herebyincorporated by reference.

BACKGROUND

In a wireless communication system, a base station may provide one ormore coverage areas, such as cells or sectors, in which the base stationmay serve user equipment devices (UEs), such as cell phones,wirelessly-equipped personal computers or tablets, tracking devices,embedded wireless communication modules, or other devices equipped withwireless communication functionality (whether or not operated by a humanuser). In general, each coverage area may operate on one or morecarriers each defining a respective bandwidth of coverage, and eachcoverage area may define an air interface providing a downlink forcarrying communications from the base station to UEs and an uplink forcarrying communications from UEs to the base station. The downlink anduplink may operate on separate carriers or may be time divisionmultiplexed over the same carrier(s). Further, the air interface maydefine various channels for carrying communications between the basestation and UEs. For instance, the air interface may define one or moredownlink traffic channels and downlink control channels, and one or moreuplink traffic channels and uplink control channels.

In accordance with the Long Term Evolution (LTE) standard of theUniversal Mobile Telecommunications System (UMTS), for instance, eachcoverage area of a base station may operate on one or more carriersspanning 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, or 20 MHz, with eachcarrier in a cover area defining a respective “cell.” On each suchcarrier used for downlink communications, the air interface then definesa Physical Downlink Shared Channel (PDSCH) as a primary channel forcarrying data from the base station to UEs, and a Physical DownlinkControl Channel (PDCCH) for carrying control signaling from the basestation to UEs. Further, on each such carrier used for uplinkcommunications, the air interface defines a Physical Uplink SharedChannel (PUSCH) as a primary channel for carrying data from UEs to thebase station, and a Physical Uplink Control Channel (PUCCH) for carryingcontrol signaling from UEs to the base station.

In LTE, downlink air interface resources are mapped in the time domainand in the frequency domain. In the time domain, LTE defines a continuumof 10-millisecond (ms) frames, divided into 1 ms sub-frames and 0.5 msslots. With this arrangement, each sub-frame is considered to be atransmission time interval (TTI). Thus, each frame has 10 TTIs, and eachTTI has 2 slots. In the frequency domain, resources are divided intogroups of 12 sub-carriers. Each sub-carrier is 15 kHz wide, so eachgroup of 12 sub-carriers occupies a 180 kHz bandwidth. The 12sub-carriers in a group are modulated together, using orthogonalfrequency division multiplexing (OFDM), in one OFDM symbol.

LTE further defines a particular grouping of time-domain andfrequency-domain resources as a downlink resource block. In the timedomain, each downlink resource block has a duration corresponding to onesub-frame (1 ms) or one slot (0.5 ms). In the frequency domain, eachdownlink resource block consists of a group of 12 sub-carriers that areused together to form OFDM symbols. Typically, a 1 ms duration of adownlink resource block accommodates 14 OFDM symbols, each spanning 66.7microseconds, with a 4.69 microsecond guard band (cyclic prefix) addedto help avoid inter-symbol interference. Depending on the bandwidth ofthe downlink carrier, the air interface may support transmission on anumber of such downlink resource blocks in each TTI. For instance, a 5MHz carrier supports 25 resource blocks in each TTI, whereas a 15 MHzcarrier supports 75 resource blocks in each TTI.

The smallest unit of downlink resources is the resource element. Eachresource element corresponds to one sub-carrier and one OFDM symbol.Thus, a resource block that consists of 12 sub-carriers and 14 OFDMsymbols has 168 resource elements. Further, each OFDM symbol and thuseach resource element can represent a number of bits, with the number ofbits depending on how the data is modulated. For instance, withQuadrature Phase Shift Keying (QPSK) modulation, each modulation symbolmay represent 2 bits; with 16 Quadrature Amplitude Modulation (16QAM),each modulation symbol may represent 4 bits; and with 64QAM, eachmodulation symbol may represent 6 bits.

Within a resource block, and cooperatively across all of the resourceblocks of the carrier bandwidth, different resource elements can havedifferent functions. In particular, a certain number of the resourceelements (e.g., 8 resource elements distributed throughout the resourceblock) may be reserved for reference signals used for channelestimation. In addition, a certain number of the resource elements(e.g., resource elements in the first one, two, or three OFDM symbols)may be reserved for the PDCCH and other control channels (e.g., aphysical hybrid automatic repeat request channel (PHICH)), and most ofthe remaining resource elements (e.g., most of the resource elements inthe remaining OFDM symbols) would be left to define the PDSCH.

Across the carrier bandwidth, each TTI of the LTE air interface thusdefines a control channel space that generally occupies a certain numberof 66.7 microsecond symbol time segments (e.g., the first one, two, orthree such symbol time segments), and a PDSCH space that generallyoccupies the remaining symbol time segments, with certain exceptions forparticular resource elements. With this arrangement, in the frequencydomain, the control channel space and PDSCH space both span the entirecarrier bandwidth. In practice, the control channel space is thentreated as being a bandwidth-wide space for carrying control signalingto UEs. Whereas, the PDSCH space is treated as defining discrete12-subcarrier-wide PDSCH segments corresponding to the sequence ofresource block across the carrier bandwidth.

One of the main functions of the PDCCH in LTE is to carry “DownlinkControl Information” (DCI) messages to served UEs. LTE defines varioustypes or “formats” of DCI messages, to be used for different purposes,such as to indicate how a UE should receive data in the PDSCH of thecurrent TTI, or how the UE should transmit data on the PUSCH in anupcoming TTI. For instance, a DCI message in a particular TTI mayschedule downlink communication of bearer data to a particular UE (i.e.,a UE-specific data transmission), by specifying one or more particularPDSCH segments that carry the bearer data in the current TTI, whatmodulation scheme is used for that downlink transmission, and so forth.And as another example, a DCI message in a particular TTI may indicatethe presence of one or more paging messages carried in particular PDSCHsegments and may cause certain UEs to read the PDSCH in search of anyrelevant paging messages.

Each DCI message may span a particular set of resource elements on thePDCCH (e.g., one, two, four, or eight control channel elements (CCEs),each including 36 resource elements) and may include a cyclic redundancycheck (CRC) that is masked (scrambled) with an identifier (e.g., aparticular radio network temporary identifier (RNTI)). In practice, a UEmay monitor the PDCCH in each TTI in search of a DCI message having oneor more particular RNTIs. And if the UE finds such a DCI message, the UEmay then read that DCI message and proceed as indicated. For instance,if the DCI message schedules downlink communication of bearer data tothe UE in particular PDSCH segments of the current TTI, the UE may thenread the indicated PDSCH segment(s) of the current TTI to receive thatbearer data.

Furthermore, a recent revision of LTE known as LTE-Advanced now permitsa base station to serve a UE with “carrier aggregation,” by which thebase station schedules bearer communication with the UE on multiplecarriers at a time. With carrier aggregation, multiple carriers fromeither contiguous frequency bands or non-contiguous frequency bands canbe aggregated to increase the bandwidth available to the UE. Currently,the maximum bandwidth for a data transaction between an eNodeB and a UEusing a single carrier is 20 MHz. Using carrier aggregation, an eNodeBmay increase the maximum bandwidth to up to 100 MHz by aggregating up tofive carriers. Each aggregated carrier is referred to as a “componentcarrier.” In some carrier-aggregation implementations, each componentcarrier will have its own control channel space (e.g., PDCCH) and itsown PDSCH space, with its control channel space carrying DCIs toschedule data transmission in its PDSCH space.

OVERVIEW

In a wireless communication system in which multiple base stationsprovide wireless coverage areas each defining a continuum of subframesdivided into time segments (such as but not limited to an LTE system),all of the base stations may be arranged by default to provide theircontrol channels (e.g., PDCCH) in the first time segments of eachsubframe and to then use the remaining time segments of each subframefor the shared channel (e.g., PDSCH). For instance, in LTE as notedabove, each base station may provide its control channel space in thefirst one, two, or three symbol time segments per subframe, leaving theremaining symbol time segments largely for use to define the PDSCH.Further, where base stations provide carrier aggregation service, theymay use this default arrangement on each of their component carriers.

A problem that can arise with this default arrangement, however, is thatcontrol channel communication in one such coverage area on a particularcarrier could interfere with control channel communication in anoverlapping coverage area on the same carrier. This problem could arisein any scenario where two or more base stations operate on the samecomponent carriers as each other and provide overlapping coverage areas.By way of example, this could occur in a scenario where a wirelessservice provider operates a macro base station (e.g., a typical celltower) that provides a wide coverage area and carrier-aggregationservice on particular component carriers and where one or more smallcell base stations (e.g., femtocells, picocells or the like) are in usewithin the macro coverage area and provide carrier-aggregation serviceon the same component carriers.

Unfortunately, such control channel interference can produce load issueswith respect to both the control channel and the shared traffic channelon a given carrier. For instance, the interference between controlchannel communications could result in UEs failing to receive controlsignaling, which could necessitate retransmission of the controlsignaling and thus lead to an increase in control channel load. Further,to the extent control signaling in particular TTIs schedules downlinkdata transmission in the same TTIs, failure to receive that controlsignaling could also mean failure to receive the associated downlinkdata transmission, which could necessitate retransmission of the dataand thus lead to an increase in traffic channel load. These issues canin turn result in reduced throughput and other undesirable conditions.Consequently, an improvement is desired.

Disclosed herein is a method and corresponding apparatus to helpovercome this problem. In accordance with one aspect of this disclosure,adjacent base stations may programmatically work with each other toarrange for their respective use of different time segments per subframefor their respective control channel use. Further, to additionally helpavoid interfering with control channel communications, each base stationmay also avoid downlink data communication in the symbol time segmentsper subframe that the other base station will be using for controlchannel communication. For instance, of the 14 OFDM symbol time segmentsin each LTE subframe, two base stations that provide overlappingcoverage may engage in signaling with each other to arrange for one ofthe base stations to use two particular ones of the symbol time segmentsfor its PDCCH and for the other base station to use two other particularones of the symbol time segments for its PDCCH, and each base stationmay exclude from its PDSCH the symbol time segments per subframe thatare designated for PDCCH use by the other base station.

Such an arrangement may help to avoid or minimize control channelinterference between the base stations. However, one drawback of thearrangement is that it may reduce the number of symbols per subframeavailable for PDSCH use, thus limiting scheduled data throughput. Thisreduced throughput may not matter for certain types of communications,such as e-mail and other short, non-real-time communications. However,it may be an issue for certain higher capacity communications andlatency-sensitive communications, such as video-streaming or gamingcommunications. Moreover, some such higher capacity communications maybe scheduled persistently (e.g., with advanced persistent orsemi-persistent scheduling) and may therefore involve less PDCCHcommunication and consequently less likelihood of control channelinterference.

In a system where base stations provide carrier-aggregation service, asolution to this problem is to apply the above process on one particularcomponent carrier but not on another component carrier and then have thebase stations select which component carrier to use for particular typesof communications based on characteristics of the communications such asdesired throughput, latency-sensitivity, and scheduling-persistence.

For instance, if we assume that both base stations providecarrier-aggregation service on the same component carriers as eachother, including a combination of a first component carrier and a secondcomponent carrier, the base stations (i) could arrange to use differenttime segments per subframe than each other for their downlink controlchannel communication on the first component carrier (and to each forgodownlink traffic channel communication in the time segments per subframeon the first component carrier that the other base station will be usingfor downlink control channel communication), but (ii) could by defaultuse the same time segments per subframe as each other for their downlinkcontrol channel communication on the second component carrier.

Based on this difference in structuring between the first componentcarrier and the second component carrier, either or each base stationmay then select a component carrier on which to schedule particular datatransmission. For example, when either or each base station is going totransmit to a UE data that is relatively high capacity (e.g.,high-throughput requirement), relatively latency-sensitive, and/orpersistently or semi-persistently scheduled, the base station mayprovide that transmission on the second component carrier, on groundsthat second component carrier may have a greater number of time segmentsper subframe available for scheduled traffic use than the firstcomponent carrier, and that such communication may not pose as much ofan issue with control channel interference and so the second componentcarrier without the base stations using different time segments persubframe for control channel communication may work fine. Whereas, wheneither or each base station is going to transmit to a UE data that isnot as high capacity, not as latency sensitive, and/or not aspersistently scheduled, the base station may provide that transmissionon the first component carrier, on grounds that first component carriermay have fewer time segments per subframe available for scheduledtraffic use and that such communication may benefit from the arrangementfor the base stations to use different time segments per subframe fortheir control channel communication.

Accordingly, in one respect, disclosed is a method operable in awireless communication system in which first and second adjacent basestations provide respective coverage areas in which to serve UEs, thebase stations being time synchronized with each other for air interfacecommunications in their respective coverage areas, each coverage areadefining a continuum of subframes each divided into a sequence of timesegments for communicating modulated data, and the second base stationproviding carrier aggregation service on component carriers.

According to the method, the first base station providescarrier-aggregation service on the same component carriers on which thesecond base station provides carrier-aggregation service, including afirst component carrier and a second component carrier. Further, thefirst base station differentially structures downlink channels on thecomponent carriers, including (i) on the first component carrier,providing control channel space in different ones of the time segmentsper subframe than time segments per subframe in which the second basestation will provide control channel space on the first componentcarrier, but (ii) on the second component carrier, providing controlchannel space in the same time segments per subframe in which the secondbase station will provide control channel space on the second componentcarrier. Based on that differential structuring of the downlink channelson the component carriers, the base station then transmits a first typeof data in traffic channel space on the first component carrier andtransmits a second type of data in traffic channel space on the secondcomponent carrier.

In another respect, disclosed is a wireless communication system thatincludes a first base station configured to provide a first coveragearea on first and second component carriers and a second base stationconfigured to provide a second coverage area also on the first andsecond component carriers, the first and second coverage areasoverlapping with each other and both defining a common continuum ofsubframes each divided into a sequence of time segments forcommunicating modulated data on the component carriers. In the disclosedsystem, the first and second base stations are configured todifferentially structure downlink channels on the first and secondcomponent carriers, including (a) engaging in signaling with each otherto arrange for (i) the first base station to use a first set of one ormore of the time segments per subframe for downlink control channelcommunication on the first component carrier, and (ii) the second basestation to use a second set of one or more of the time segments persubframe for downlink control channel communication on the firstcomponent carrier, but (b) both base stations being configured to usethe same time segments per subframe as each other for downlink controlchannel communication on the second component carrier. Further, thefirst and second base stations are configured, based on the differentialstructuring of the downlink channels on the first and second componentcarriers, to transmit a first type of data in downlink traffic channelspace on the first component carrier and to transmit a second type ofdata in downlink traffic channel space on the second component carrier.

In still another respect, disclosed is a base station arranged to carryout various features of the disclosed method. The base station includesa wireless communication interface configured to provide a wirelesscoverage area in which to serve UEs with carrier-aggregation service ona plurality of component carriers including a first component carrierand a second component carrier, where, on each component carrier, thecoverage area defining a continuum of subframes each divided into asequence of time segments for communicating modulated data. Further, thebase station includes a controller configured to manage use of timesegments per subframe in accordance with the disclosure.

In particular, the controller is configured to differentially structuredownlink channels on the component carriers, including (i) on the firstcomponent carrier, providing control channel space in different ones ofthe time segments per subframe than time segments per subframe in whichan adjacent second base station will provide control channel space onthe first component carrier, but (ii) on the second component carrier,providing control channel space in the same time segments per subframein which the adjacent second base station will provide control channelspace on the second component carrier. Further, the controller isconfigured, based on the differential structuring of the downlinkchannels on the component carriers, (i) to cause the base station totransmit a first type of data in traffic channel space on the firstcomponent carrier due to the first type of data being of the first type,and (ii) to cause the base station to transmit a second type of data inthe traffic channel space on the second component carrier due to thesecond type of data being of the second type.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description, with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescriptions provided in this overview and below are intended toillustrate the invention by way of example only and not by way oflimitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example wirelesscommunication system in which features of the present disclosure can beimplemented.

FIG. 2 is an illustration of a portion of an example continuum ofsubframes.

FIG. 3 is an illustration of an example subframe, depicting an examplesequence of time segments within the subframe.

FIG. 4 is an illustration of time synchronized subframes of adjacentbase station coverage areas, showing potentially interfering controlchannel space in the coverage areas.

FIG. 5 is an illustration of time synchronized subframes of adjacentbase station coverage areas but with the coverage areas using differenttime segments than each other for control channel space.

FIG. 6 is an illustration of example differential structuring ofcomponent carriers in accordance with the disclosure.

FIG. 7 is a flow chart depicting example operations in accordance withthe disclosure.

FIG. 8 is a simplified block diagram of an example base station operablein accordance with the disclosure.

DETAILED DESCRIPTION

The present method and apparatus will be described herein in the contextof LTE. However, it will be understood that principles of the disclosurecan extend to apply in other scenarios as well, such as with respect toother air interface protocols. Further, even within the context of LTE,numerous variations from the details disclosed herein may be possible.For instance, elements, arrangements, and functions may be added,removed, combined, distributed, or otherwise modified. In addition, itwill be understood that functions described here as being performed byone or more entities may be implemented in various ways, such as by aprocessor executing software instructions for instance.

Referring to the drawings, as noted above, FIG. 1 is a simplified blockdiagram of an example wireless communication system in which features ofthe present disclosure can be implemented. In particular, FIG. 1 depictsa representative LTE network 10, which functions primarily to serve UEswith wireless packet data communication service, including possiblyvoice-over-packet service, but may also provide other functions. Asshown, the LTE network includes two representative LTE base stations(evolved Node-Bs (eNodeBs)) 12, 14, each of which would have an antennastructure and associated equipment for providing a respective LTEcoverage area in which to serve UEs. By way of example, eNodeB 12 isshown providing a coverage area 16 in which to serve one or more UEs 18,and eNodeB 14 is shown providing a coverage area 20 in which to serveone or more UEs 22. The UEs may take various forms, such as any of thosenoted above, whether or not operated by a human “user.”

In practice, these base stations may be adjacent to each other in thewireless communication system. This adjacent relationship between thebase stations could be defined in various ways. For instance, the basestations could be considered adjacent to each other if the basestations' respective coverage areas overlap with each other in whole orin part, as may be established by one or more UEs served by one of thebase stations reporting to the serving base station that the UE(s) aredetecting signals from the other base station. Alternatively oradditionally, the base stations could be considered adjacent to eachother simply if at least one of the base stations lists the other basestation on a neighbor list useable to manage handover of UEs between thebase stations. Physically, the base stations can be co-located ordistributed at some distance from each other.

Further, the base stations themselves can take various forms. By way ofexample, either or each base station could be a macro base station ofthe type typically provided by a wireless service provider with a towermounted antenna structure and associated equipment. Or either or eachbase station could be a small cell base station (such as a femtocell,picocell, or the like) typically provided to help improve coveragewithin macro cell coverage and usually having a much smaller form factorand coverage range than a macro base station. As a specific example,base station 12 could be a macro base station, and base station 14 couldbe a small cell base station positioned at least partially withincoverage of the macro base station. Thus, the two base stations wouldprovide overlapping coverage.

As further shown in the example arrangement of FIG. 1, the base stationshave a communication interface (e.g., an LTE “X2” interface) with eachother, and each base station has a communication interface with amobility management entity (MME) 24 that functions as a signalingcontroller for the LTE network and may also facilitate communicationbetween the base stations. Further, each base station then has acommunication interface with a serving gateway (SGW) 26, which in turnhas a communication interface with a packet-data network gateway (PGW)28 that provides connectivity with a packet-switched network 30, and theMME 24 has a communication interface with the SGW 26. In practice, theillustrated components of the LTE network may sit as nodes on a privatepacket-switched network owned by an operator of the LTE network, andthus the various communication interfaces may be logical interfacesthrough that network.

In the example arrangement, each base station serves one or more UEswith carrier-aggregation service on a plurality of component carriers,meaning that each base station serves at least one UE concurrently onmultiple component carriers. FIG. 1 depicts such an arrangement whereeach base station 12, 14 provides such carrier aggregation service on acombination of component carrier CC1 and component carrier CC2. Each ofthese component carriers may have a respective bandwidth (such as 5 MHzor another carrier bandwidth as discussed above). The carrieraggregation service provided by either base station could also encompassone or more additional component carriers. But, for simplicity, thisdisclosure will address the scenario where the adjacent base stationsboth provide carrier-aggregation on the same component carriersincluding CC1 and CC2, and thus where both base stations may communicateon the same CC1 resources as each other (in time and frequency) and bothbase stations may communicate on the same CC2 resources as each other(in time and frequency).

As noted above, each base station's coverage area may then define acontinuum of subframes in the time domain, with each subframe beingdivided into a sequence of time segments for communicating modulateddata. Further, the base stations may be time synchronized with eachother, so that their subframes and time segments within their subframesoccur at the same time as each other (possibly with minor tolerance forvariation). Thus, each base station's coverage area would start a newsubframe at the same time as the other base station's coverage area, andthe time segments within a subframe of one base station's coverage areawould be aligned in time with the time segments of the other basestation's coverage area. This time synchronization could be establishedby use of GPS timing or another mechanism.

FIG. 2 depicts a portion of an example continuum of subframes in arepresentative LTE coverage area, shown within a portion of one examplecomponent-carrier bandwidth. As illustrated in FIG. 2, the subframes ofthe continuum are 1 ms each, and the continuum would continue before andafter the portion of time shown. Although the continuum is shown with noseparation between the subframes, the continuum could just as well bedefined with separation between the subframes. For instance, every other1 ms could define a next subframe, or some other repeating pattern coulddefine occurrences of subframes.

FIG. 3 next depicts an example of one of the subframes, also shownwithin a portion of the example component-carrier bandwidth. Asillustrated in FIG. 3, the example subframe is divided over time into asequence of 14 symbol time segments labeled A through N in their orderof occurrence, each of which may be 66.7 microseconds or the like. Aswith the subframe timing, although the sequence of these time segmentsis shown with one time segment right after another and with the sequenceof time segments spanning the full duration of the subframe, thesequence could be defined in other ways, such as including just certaintime segments within the subframe. In practice, the illustrated sequenceof time segments may repeat for each successive subframe of thecontinuum of subframes.

As discussed above, in a typical LTE implementation, the first one, two,or three symbol time segments in each subframe would be used to definedownlink control channel space (e.g., for PDCCH and PHICHcommunication), and the remaining symbol time segments in each subframewould then be used to define downlink shared channel space (e.g., forPDSCH communication), with the understanding that certain resourceelements would be reserved for other purposes (such as to carryreference signals for instance).

As further noted above, however, a problem could arise where twoadjacent base stations use the same time segments per subframe for theirdownlink control channel communication on a particular componentcarrier. FIG. 4 depicts such a situation way of example. In particular,FIG. 4 shows concurrent control-channel subframes of base stations 12and 14 on the example component carrier. In this arrangement, both basestations use time segments A and B per subframe as their respectivedownlink control channel space (e.g., for PDCCH and PHICH communication)and both base stations use the remaining time segments C through N persubframe as their respective downlink traffic channel space (e.g., forPDSCH communication). Since the base stations are operating on the samecomponent carrier and provide overlapping coverage, the result of thisarrangement may well be interference between their control channelcommunications, leading to issues such as those noted above.

To help overcome this problem, the present disclosure provides for thebase stations to work with each other (e.g., to engage in inter-basestation signaling with each other) so as to arrange for their use ofdifferent time segments than each other per subframe for theirrespective downlink control channel communication on a given componentcarrier, and for each base station to not use for downlink controlchannel communication the time segments that the other base station willbe using for downlink control channel communication on that componentcarrier. Further, to additionally help avoid interference with controlchannel communication on that component carrier, each base station mayalso operate to avoid using for downlink traffic channel communicationon the component carrier the time segments that the other base stationwill be using for downlink control channel communication on thecomponent carrier in accordance with the arrangement for the basestations to use different ones of the time segments per subframe fortheir respective downlink control channel communication on the componentcarrier.

In practice, for instance, base station 12 may select one or more timesegments for base station 12 to use per subframe for downlink controlchannel communication on the component carrier and may transmit a signalto base station 14, notifying base station 14 that base station 12 willbe using the selected time segment(s) for downlink control channelcommunication on the component carrier. (The selected time segments persubframe could be contiguous, as is the case with the default LTEcontrol channel space, or could be non-contiguous.) Further, basestation 14 may select one or more other time segments for base station14 to use per subframe for downlink control channel communication on thecomponent carrier, perhaps in response to the signal from base station12, and may transmit a signal to base station 12 notifying base station12 that base station 14 will be using the selected time segment(s) fordownlink control channel communication on the component carrier.Alternatively, this arrangement process could have one of the basestations managing the allocation of time segments between the basestations for downlink control channel use, such as directing the otherbase station which time segments per subframe to use, and/or couldinvolve input or directives from one or more other entities, such as MME24 for instance.

With the agreement in place for one base station to use one set of timesegment(s) per subframe for downlink control channel communication onthe component carrier and for an adjacent other base station to use adifferent (mutually exclusive) set of time segment(s) per subframe fordownlink control channel communication on the same component carrier,each base station may then engage in downlink control channelcommunication accordingly on the component carrier. In particular, eachbase station may provide its downlink control channel communication onthe component carrier in the time segment(s) that it is set to use fordownlink control channel communication on the component carrier and notin the time segment(s) that the adjacent base station is set to use fordownlink control channel communication on the component carrier.Further, each base station may also forgo engaging in downlink trafficchannel communication on the component carrier in the time segment(s)that the adjacent base station is set to use for downlink controlchannel communication on the component carrier.

In addition, each base station may notify its served UEs which timesegment(s) will be used for downlink control channel communication onthe component carrier, so that the UEs can receive control channelcommunications per subframe in the indicated time segment(s) on thecomponent carrier. For instance, each base station may broadcast orotherwise transmit in its coverage area a system message, such as an LTEsystem information block (SIB), that specifies which time segment(s) persubframe the base station will use for downlink control channelcommunication on the component carrier. Provided with that information,served UEs may then scan for downlink control channel communication inthe indicated time segment(s) on the component carrier rather thanmerely defaulting to use of the first one, two, or thee time segmentsper subframe as downlink control channel space on the component carrier.For instance, a UE may search for DCIs and HARQ messages in theindicated time segments on the component carrier.

FIG. 5 illustrates one of many possible arrangements for use of timesegments per subframe as between adjacent base stations in accordancewith this process. In particular, FIG. 5 depicts the same subframesegments shown in FIG. 4, but depicts base station 12 as being set touse time segments A and B as its downlink control channel space, andbase station 14 as being set to use time segments C and D as itsdownlink control channel space. (Although this example shows the basestations as using time segments at the start of a subframe, each basestation in this process could be set to use various time segments persubframe. For instance, one base station could use time segments C andD, and the other base station could use time segments F and G. Further,as noted above, the time segments that a base station uses need not becontiguous.)

With this arrangement, base station 12 could then use remaining timesegments C through N as its downlink traffic channel space, but basestation 12 may advantageously forgo downlink traffic channeltransmission in time segments C and D to help further reduce controlchannel interference for base station 14. Likewise, base station 14could use remaining time segments A, B, and E through N as its downlinktraffic channel space, but base station 14 may advantageously forgodownlink traffic channel transmission in time segments A and B to helpfurther reduce control channel interference for base station 12. Tofacilitate this, when each base station allocates a particular resourceblock to a UE for downlink traffic channel communication, the basestation may just not transmit in the time segments that the other basestation is set to use for downlink control channel communication but mayrestrict its downlink traffic channel communication to the otherremaining time segments.

In practice, this method can be applied with respect to various pairs ofbase stations in a representative wireless communication system.Further, the process in such a system could be iterative and couldinvolve negotiation, accounting for the fact that a given base stationmay be adjacent to more than one other base station.

For instance, consider a scenario where a first base station sitsbetween a second base station and a third base station. Through thepresent process, the first base station may determine that the secondbase station will be using particular time segments per subframe fordownlink control channel communication on a given component carrier(e.g., by receiving a signal from the second base station indicating so,or by directing the second base station accordingly), and the first basestation may responsively opt to use different time segments per subframefor downlink control channel communication on that component carrier.Further, the first base station may notify the third base station of thetime segments per subframe that the first base station is going to usefor downlink control channel communication on the component carrier andmay similarly determine which time segments per subframe the second basestation is going to use for downlink control channel communication onthe component carrier, possibly one or more of the time same timesegments that the second base station will be using for downlink controlchannel communication on the component carrier. Furthermore, in thisarrangement, the first base station may then also forgo downlink trafficchannel communication on the component carrier in both the one or moretime segment(s) per subframe that the second base station is set to usefor downlink control channel communication on the component carrier andin one or more time segment(s) per subframe that the third base stationis set to use for downlink control channel communication on thecomponent carrier.

With the present method applied on a particular component carrier, eachbase station may have a reduced extent of downlink traffic channelcapacity, as each base station forgoes downlink traffic channelcommunication on the component carrier in the time segment(s) that oneor more adjacent base stations will be using for downlink controlchannel communication on the component carrier. This may be fine in ascenario where the base station is not experiencing a high demand fordownlink traffic channel communication on the component carrier. In ascenario where the base station experiences a threshold high level ofload for downlink traffic channel communication on the component carrier(e.g., when its downlink data buffer for communication on the componentcarrier becomes more than a predefined high percentage full), the basestation may then transition to provide downlink traffic channelcommunication on the component carrier in one or more of the timesegment(s) that an adjacent base station is set to use for downlinkcontrol channel communication on the component carrier.

Further, in a scenario where the base station at issue has more than oneadjacent base station, the base station may intelligently select one ofthe adjacent base stations for this purpose based on a consideration ofload (perhaps specifically on the component carrier at issue) of each ofthe adjacent base stations. For instance, the base station may receive(perhaps regularly) indicia of load of the adjacent base stations, suchas a report from each adjacent base station indicating its level ofdownlink control channel load and/or downlink traffic channel load(perhaps component-carrier specific). The base station at issue may thenselect the adjacent base station having the lowest indicated level ofload (considering downlink control channel load and/or downlink trafficchannel load), as being the adjacent base station that may be able tobest withstand added downlink control channel interference on thecomponent carrier. And the base station at issue may then transition toadd to its set of time segments for downlink traffic channelcommunication on the component carrier one or more of the time segmentsthat the selected adjacent base station is set to use for downlinkcontrol channel communication on the component carrier, possibly whilecontinuing to avoid downlink traffic channel communication on thecomponent carrier in any time segment(s) that one or more adjacent basestations would be using for downlink control channel communication onthe component carrier.

In addition, having each base station forgo downlink traffic channelcommunication in the time segments that one or more adjacent basestations will be using for downlink control channel communication couldpose an issue for certain types of data communications more than forothers. For example, data communications that involve a lot of databeing communicated at a high data rate, such as streaming video orgaming communications, may benefit from more traffic channel capacityand may experience reduced quality if there is insufficient trafficchannel capacity. Likewise, latency-sensitive traffic such as real-timemedia streams may similarly benefit from higher traffic channel capacityand face issues with low traffic channel capacity. On the other hand,relatively small, connectionless or non-real-time communications such ase-mail communications or other best-efforts traffic may not suffer anyperceivable problem when faced with traffic channel congestion.

Moreover, having the adjacent base stations use different time segmentsper subframe for their respective downlink control channelcommunications may benefit certain types of data communications morethan others. For example, certain types of data, such as voice-over-IPdata and streaming video data for instance, may be fairly persistent(i.e., ongoing or regularly transmitted), and a base station may be setto engage in persistent or semi-persistent scheduling of downlinktransmission of such data. Such persistent or semi-persistent schedulingmay involve transmitting to a UE a DCI that specifies a repeatscheduling directive, such as an indication that downlink transmissionto the UE will occur in particular PDSCH resource blocks everyparticular number subframes or the like. Such persistent orsemi-persistent scheduling may thus involve less control channeltransmission overall, and may thus give rise to less likelihood ofcontrol channel interference between the base stations' coverage areas.Consequently, the present method may be less beneficial for suchpersistent or semi-persistent data communication. On the other hand,data communication that is less persistent, such as variousconnectionless and other best-efforts traffic, may benefit more from thepresent process.

Given these considerations, the present disclosure additionally providesfor differentially structuring various component carriers on whichadjacent base stations each serve one or more UEs withcarrier-aggregation service, such as on CC1 and CC2 for instance, andallocating transmission of certain types of data to certain componentcarriers accordingly. In particular, in a scenario where adjacent basestations each serve one or more respective UEs on at least the samecombination of component carriers CC1 and CC2, the base stations mayapply the above process on CC1 but not on CC2 so that (i) the basestations would use different time segments per subframe than each otherfor downlink control channel communication on CC1, and may each forgodownlink traffic channel communication on CC1 in the time segments persubframe that the other base station will use for downlink controlchannel communication on CC1, but (ii) the base stations would use thesame time segments per subframe as each other for downlink controlchannel communication on CC2 (e.g., both using at least the first one,two, or three default starting time segments per subframe for downlinkcontrol channel communication).

The result of this differential structuring may then be that the basestations may experience reduced control channel interference on CC1 butnot on CC2, and that the base stations may have reduced traffic channelcapacity (over time) on CC1 but not on CC2. With such an arrangement, inview of the considerations above, the base stations may thenintentionally schedule less persistent and/or lower capacity data onCC1, and the base station may intentionally schedule more persistentand/or higher capacity data on CC2.

FIG. 6 depicts this arrangement by way of example. The illustrationdepicts at the top a comparison of CC1 time segment allocations of basestation 12 and base station 14 and at the bottom a comparison of CC2time segments allocation of base stations 12 and 14. Although the topand bottom depictions both represent a sequence of time segments fromtop down, it should be understood that the CC1 time segments would byaligned in time (concurrent) with the CC2 time segments. Due to spaceconstraints for the figure, the top and bottom depictions are not shownside by side.

As shown in this example, the base stations are arranged to usedifferent time segments than each other for their downlink controlchannel communication on CC1 and to not use for downlink traffic channelcommunication on CC1 the time segments that the other base station isset to use for downlink control channel communication on CC1. Further,as shown in the example, the base stations are arranged to use the sametime segments as each other for their downlink control channelcommunication on CC2. (In practice, the number of time segments that thebase stations use for downlink control channel communication on CC2 maydiffer between the base stations. For instance one base station may usethe first two time segments per subframe, and the other may use thefirst three time segments per subframe. But the point here would be thatthe base stations would not arrange to use different time segments thaneach other per the above process.)

To facilitate this in practice, the base stations may provide theirrespective served UEs with a control message, such as a SIB message,that specifies the time segments per subframe that will be used fordownlink control channel communication on CC1, whereas the base stationsmay provide their served UEs with a different control message, such as aphysical control format indicator (PCFICH) value that specifies how manyof the starting time segments per subframe on CC2 will be used fordownlink control channel communication. In a carrier aggregationarrangement, a base station could provide these or other such controlmessages for each component carrier on that component carrier, or thebase station could provide these or other such control messages for thecomponent carriers on a given one of the component carriers, such as onthe PCell. Other arrangements are possible as well.

This arrangement thus involves each base station differentiallystructuring the component carriers, by having different time segmentsthan the other base station for downlink control channel communicationon CC1 but having at least the same time segments as the other basestation for downlink control channel communication on CC2.

Given this differential structuring of the component carriers and theconsiderations above, each base station may then intentionally scheduleless persistent and/or lower capacity data (such as e-mail or otherconnectionless or best-efforts data) in resource blocks or otherfrequency segments on CC1 (and perhaps forgo scheduling such data onCC2) and may intentionally schedule more persistent and/or highercapacity data (such as voice-over-IP data and streaming video data forinstance) in resource blocks or other frequency segments on CC2 (andperhaps forgo scheduling such data on CC1).

Note that with this arrangement, each base station would still beserving a respective given UE with carrier-aggregation service even ifthe UE is currently engaged in communication of just a particular typeof data and thus if the base station is currently schedulingtransmission of that data on just one of the component carriers. Thefact of carrier-aggregation service may be established by the basestation directing the UE to operate on the multiple component carriers(e.g., CC1 and CC2), with an RRC connection message for instance, inwhich case the UE may then be set to monitor control channel space onboth component carriers—even though at the moment the base station isscheduling data transmission to the UE on just one of the componentcarriers. Further, with the same arrangement, a base station couldconcurrently transmit one type of data to the UE on CC1 and another typeof data to the UE on CC2.

FIG. 7 is next a flow chart depicting operations that can be carried outin accordance with the present disclosure, in a wireless communicationsystem in which first and second adjacent base stations providerespective coverage areas in which to serve UEs, the base stations beingtime synchronized with each other for air interface communications intheir respective coverage areas, each coverage area defining a continuumof subframes each divided into a sequence of time segments forcommunicating modulated data, and the first and second base stationsboth provide carrier-aggregation service on component carriers includinga first component carrier and a second component carrier.

As shown in FIG. 7, at block 70, the first base station differentiallystructures downlink channels on the component carriers, including (i) onthe first component carrier, providing control channel space indifferent ones of the time segments per subframe than time segments persubframe in which the second base station will provide control channelspace on the first component carrier, but (ii) on the second componentcarrier, providing control channel space in the same time segments persubframe in which the second base station will provide control channelspace on the second component carrier. Further, at block 72, based onthe differential structuring of the downlink channels on the componentcarriers, the first base station transmits a first type of data intraffic channel space on the first component carrier and transmits asecond type of data in traffic channel space on the second componentcarrier.

In line with the discussion above, the act of the first base stationproviding control channel space on the first component carrier indifferent ones of the time segments than time segments in which thesecond base station will provide control channel space on the firstcomponent carrier may take various forms. For instance, it may involvedetermining that the second base station will use particular ones of thetime segments per subframe for downlink control channel communication onthe first component carrier, and then, based on that determination, thefirst base station setting itself (i) to use one or more different onesof the time segments, other than the particular time segments, persubframe for downlink control channel communication on the firstcomponent carrier and (ii) to avoid downlink traffic channelcommunication in the one or more particular time segments per subframeon the first component carrier.

Further, the time segments per subframe in which the second base stationwill provide control channel space on the second component carrier aredefault control channel space time segments, such as a designated numberof time segments starting at the beginning of each subframe. And in thatcase, the act of providing control channel space on the second componentcarrier in the same time segments per subframe in which the second basestation will provide control channel space on the second componentcarrier may involve providing control channel space on the secondcomponent carrier in the default control channel space time segments.

Moreover, as a supplement to this process, the first base station couldcarry out the above-discussed variation in which, when the first basestation detects a threshold high level of load for downlink trafficchannel communication, the first base station may transition to beginproviding downlink traffic channel communication in one or more timesegments that the second base station will be using for downlink controlchannel communication. With the carrier-aggregation implementation, thefirst base station could do this specifically on CC1, and the thresholdhigh level of load could take various forms, such as a threshold highlevel of load for downlink traffic channel communication by the firstbase station of the first type of data, such as a threshold high extentof the first type data to be transmitted to one or more UEs, and/or athreshold high level of congestion on CC1 in other ways.

FIG. 8 is next a simplified block diagram of an example base station,showing some of the components of such a base station to facilitateoperation in accordance with the present disclosure, with theunderstanding that numerous variations are possible. As shown in FIG. 8,the example base station includes a wireless communication interface 80,a network interface (backhaul interface) 82, and a controller 84, withvarious ones of these or other components being communicatively linkedtogether by a system bus, network, or other connection mechanism 76 orperhaps integrated together to some extent.

Wireless communication interface 80 may comprise a power amplifier 88,cellular transceiver 90, and antenna structure 92 and may function incombination to provide a coverage area with an air interface asdescribed above. As such, the wireless communication interface 80 may beconfigured to receive data, generate symbols from the data, and transmitthe symbols on the air interface, and to define on the air interfacevarious channels such as a PDCCH and PDSCH as discussed above. Networkinterface 82 may then comprise a wired and/or wireless networkcommunication interface (such as an Ethernet interface) through whichthe base station may communicate with other base stations and withvarious other network entities in line with the discussion above.

Controller 84, which may be integrated with transmitter 80 or one ormore other components and may comprise one or more processing unitsprogrammed with instructions to carry out various functions, may thencontrol the transmission of data, including control and user data, onthe downlink air interface. For example, controller 84 may allocatedownlink resource blocks to UEs and generate corresponding DCI messages,and controller 84 may control transmission by transmitter 80accordingly. Further, controller 84 may implement features of thepresent method as discussed above, to manage which of the time segmentsper subframe the base station uses for downlink control channelcommunication and which of the time segments per subframe the basestation uses for downlink traffic channel communication. Thus, the basestation including such a controller would be configured to carry outsuch features.

With such an arrangement, in line with the discussion above, thecontrollers of adjacent first and second base stations may be configuredto differentially structure downlink channels on the first and secondcomponent carriers on which the base stations both provide carrieraggregation service, with the differential structuring including (a)engaging in signaling with each other to arrange for (i) the first basestation to use a first set of one or more of the time segments persubframe for downlink control channel communication on the firstcomponent carrier, and (ii) the second base station to use a second setof one or more of the time segments per subframe for downlink controlchannel communication on the first component carrier, but (b) both basestations being configured to use the same time segments per subframe aseach other for downlink control channel communication on the secondcomponent carrier. Further, the controllers of both base station may beconfigured, based on the differential structuring of the downlinkchannels on the first and second component carriers, to transmit a firsttype of data in downlink traffic channel space on the first componentcarrier (i.e., to schedule such transmission) and to transmit a secondtype of data in downlink traffic channel space on the second componentcarrier (i.e., to schedule such transmission).

Exemplary embodiments have been described above. Those skilled in theart will understand, however, that changes and modifications may be madeto these embodiments without departing from the true scope and spirit ofthe invention.

We claim:
 1. In a wireless communication system in which first and second adjacent base stations provide respective coverage areas in which to serve user equipment devices (UEs), wherein the base stations are time synchronized with each other for air interface communications in their respective coverage areas, each coverage area defining a continuum of subframes each divided into a sequence of time segments for communicating modulated data, wherein the second base station provides carrier aggregation service on component carriers, a method comprising: providing, by the first base station, carrier-aggregation service on the same component carriers on which the second base station provides carrier-aggregation service, the component carriers including a first component carrier and a second component carrier; differentially structuring downlink channels on the component carriers, by the first base station, including (i) on the first component carrier, providing control channel space in different ones of the time segments per subframe than time segments per subframe in which the second base station will provide control channel space on the first component carrier, but (ii) on the second component carrier, providing control channel space in the same time segments per subframe in which the second base station will provide control channel space on the second component carrier; and based on the differential structuring of the downlink channels on the component carriers, transmitting by the first base station a first type of data in traffic channel space on the first component carrier and transmitting by the first base station a second type of data in traffic channel space on the second component carrier.
 2. The method of claim 1, wherein providing control channel space on the first component carrier in different ones of the time segments than time segments in which the second base station will provide control channel space on the first component carrier comprises: determining that the second base station will use particular ones of the time segments per subframe for downlink control channel communication on the first component carrier, and based on the determination that the second base station will use the particular time segments per subframe for downlink control channel communication on the first component carrier, the first base station setting itself (i) to use one or more different ones of the time segments, other than the particular time segments, per subframe for downlink control channel communication on the first component carrier and (ii) to avoid downlink traffic channel communication in the one or more particular time segments per subframe on the first component carrier.
 3. The method of claim 2, wherein the time segments per subframe in which the second base station will provide control channel space on the second component carrier are default control channel space time segments, and wherein providing control channel space on the second component carrier in the same time segments per subframe in which the second base station will provide control channel space on the second component carrier comprises providing control channel space on the second component carrier in the default control channel space time segments.
 4. The method of claim 3, wherein the default control channel space time segments are a designated number of time segments starting at a beginning of each subframe.
 5. The method of claim 2, wherein each component carrier defines a respective frequency bandwidth, each respective frequency bandwidth defining, per subframe, a sequence of frequency segments for carrying downlink traffic channel communication, the method further comprising: allocating, by the first base station, one or more of the frequency segments in a given subframe on the first component carrier for downlink traffic channel communication of the first type of data, wherein, due to the avoiding of downlink traffic channel communication in the one or more particular time segments per subframe on the first component carrier, the first base station limits downlink traffic channel communication in the allocated one or more frequency segments to be in just one or more time segments other than the one or more particular time segments.
 6. The method of claim 2, further comprising: detecting by the first base station a threshold high level of load for downlink traffic channel communication by the first base station of the first type of data; and responsive to detecting the threshold high level of load, transitioning by the first base station to provide downlink traffic channel communication on the first component carrier in the one or more time segments that the first base station determined the second base station will use for downlink control channel communication.
 7. The method of claim 2, wherein determining that the second base station will use particular ones of the time segments per subframe for downlink control channel communication on the first component carrier comprises: engaging in inter-base-station signaling with the second base station to make an arrangement for the first base station and the second base station to use different ones of the time segments per subframe for their respective downlink control channel communication on the first component carrier, wherein avoiding downlink traffic channel communication in the one or more particular time segments based on the determination that that the second base station will use the particular time segments per subframe for downlink control channel communication on the first component carrier comprises avoiding downlink traffic channel communication in one or more time segments that the particular second base station will use for control channel communication on the first component carrier in accordance with the arrangement for the first base station and particular second base station to use different ones of the time segments per subframe for their respective control channel communication on the first component carrier.
 8. The method of claim 1, further comprising: providing, by the first base station, to one or more UEs served by the first base station, an indication of which one or more time segments per subframe the first base station will be using for downlink control channel communication on the first component carrier, to enable the one or more UEs served by the first base station to receive downlink control channel communication from the first base station in the indicated one or more time segments per subframe on the first component carrier.
 9. The method of claim 1, wherein each base station's provided coverage area defines an orthogonal frequency division multiple access air interface, and wherein the time segments are symbol time segments.
 10. The method of claim 8, wherein downlink control channel communication comprises physical downlink control channel (PDCCH) communication.
 11. The method of claim 1, transmitting the first type of data in traffic channel space on the first component carrier and transmitting the second type of data in traffic channel space on the second component carrier is based at least in part on the first type of data being less persistently scheduled than the second type of data.
 12. A wireless communication system comprising: a first base station configured to provide a first coverage area on first and second component carriers, wherein the first coverage area defines a continuum of subframes each divided into a sequence of time segments for communicating modulated data on the component carriers; and a second base station configured to provide a second coverage area on the same first and second component carriers, wherein the second coverage area defines the same continuum of subframes each divided into the sequence of time segments for carrying modulated data, wherein the first coverage area overlaps with the second coverage area, and wherein the base stations are time synchronized with each other for air interface communications in their respective coverage areas, wherein the first and second base stations are configured to differentially structure downlink channels on the first and second component carriers, wherein differentially structuring downlink channels on the first and second component carriers comprises (a) engaging in signaling with each other to arrange for (i) the first base station to use a first set of one or more of the time segments per subframe for downlink control channel communication on the first component carrier, and (ii) the second base station to use a second set of one or more of the time segments per subframe for downlink control channel communication on the first component carrier, but (b) both base stations being configured to use the same time segments per subframe as each other for downlink control channel communication on the second component carrier, and wherein, the first and second base stations are further configured, based on the differential structuring of the downlink channels on the first and second component carriers, to transmit a first type of data in downlink traffic channel space on the first component carrier and to transmit a second type of data in downlink traffic channel space on the second component carrier.
 13. The wireless communication system of claim 12, wherein the first base station is configured to transmit to the second base station a signal indicating that the first base station will use the first set of one or more of the time segments per subframe for downlink control channel communication on the first component carrier and to receive from the second base station a signal indicating that the second base station will use the second set of one or more of the time segments per subframe for downlink control channel communication on the first component carrier, and wherein the second base station is configured to receive from the first base station the signal indicating that the first base station will use the first set of one or more of the time segments per subframe for downlink control channel communication on the first component carrier and to transmit to the first base station the signal indicating that the second base station will use the second set of one or more of the time segments per subframe downlink control channel communication on the first component carrier.
 14. The wireless communication system of claim 13, wherein the first base station is configured to respond to the signal received from the second base station by avoiding use of the second set of one or more of the time segments per subframe for downlink traffic channel communication on the first component carrier, and wherein the second base station is configured to respond to the signal received from the first base station by avoiding use of the first set of one or more of the time segments per subframe for downlink traffic channel communication on the first component carrier.
 15. The wireless communication system of claim 14, wherein each of the first and second component carriers defines a respective frequency bandwidth, each respective frequency bandwidth defining, per subframe, a sequence of frequency segments for carrying downlink traffic channel communication, wherein the first base station avoiding use of the second set of time segments per subframe for downlink traffic channel communication on the first component carrier comprises, in one or more downlink resource blocks allocated by the first base station for carrying downlink traffic channel communication on the first component carrier, the first base station limiting downlink traffic channel communication to just one or more time segments other than the second set of time segments, and wherein the second base station avoiding use of the first set of time segments per subframe for downlink traffic channel communication on the first component carrier comprises, in one or more downlink resource blocks allocated by the second base station for carrying downlink traffic channel communication on the first component carrier, the second base station limiting downlink traffic channel communication to just one or more time segments other than the first set of time segments.
 16. The wireless communication system of claim 12, wherein the first base station is further configured to notify one or more user equipment devices (UEs) served by the first base station that the first base station will provide downlink control channel communication on the first component carrier in the first set of one or more of the time segments, and wherein the second base station is further configured to notify one or more UEs served by the second base station that the second base station will provide downlink control channel communication on the first component carrier in the second set of one or more of the time segments.
 17. The wireless communication system of claim 12, wherein the first base station is further configured to detect a threshold high level of load for downlink traffic channel communication from the first base station on the first component carrier and, responsive to detecting the threshold high level of load for downlink traffic channel communication from the first base station on the first component carrier, to transition to begin providing downlink traffic channel communication in the second set of one or more of the time segments on the first component carrier.
 18. The wireless communication system of claim 17, wherein each of the first and second coverage areas defines an orthogonal frequency division multiple access air interface, wherein the time segments are symbol time segments, wherein the downlink control channel communication comprises physical downlink control channel (PDCCH) communication, and wherein downlink traffic channel communication comprises physical downlink shared channel (PDSCH) communication.
 19. The wireless communication of claim 12, wherein the transmitting of the first type of data in downlink traffic channel space on the first component carrier and of the second type of data in downlink traffic channel space on the second component carrier is based further on the first type of data being less persistently scheduled than the second type of data.
 20. A first base station comprising: a wireless communication interface configured to provide a wireless coverage area in which to serve user equipment devices (UEs) with carrier-aggregation service on a plurality of component carriers including a first component carrier and a second component carrier, wherein, on each component carrier, the coverage area defines a continuum of subframes each divided into a sequence of time segments for communicating modulated data; and a controller configured to differentially structure downlink channels on the component carriers, including (i) on the first component carrier, providing control channel space in different ones of the time segments per subframe than time segments per subframe in which an adjacent second base station will provide control channel space on the first component carrier, but (ii) on the second component carrier, providing control channel space in the same time segments per subframe in which the adjacent second base station will provide control channel space on the second component carrier, wherein the first base station and the adjacent second base station are time synchronized with each other for air interface communications, and wherein the controller is configured, based on the differential structuring of the downlink channels on the component carriers, (i) to cause the base station to transmit a first type of data in traffic channel space on the first component carrier due to the first type of data being of the first type, and (ii) to cause the base station to transmit a second type of data in the traffic channel space on the second component carrier due to the second type of data being of the second type. 